Reflex, magnifying optical system

Abstract

A first lens group in a reflex, magnifying optical system includes sequentially from the side of an object, a first lens that has a negative refractive power and is a meniscus lens having a concave aspect facing toward an image, an optical element (prism) that refracts an optical path, a second lens having a negative refractive power and a concave aspect facing toward the object, and a third lens having a positive refractive power. A portion of an image-side aspect of the first lens abuts a plane of incidence of the optical element. A portion of an object-side aspect of the second lens abuts a plane of transmission of the optical element.

1. A reflex, magnifying optical system that is a variable-magnification optical system having a plurality of lens groups and varying magnification by moving any of the lens groups, the reflex, magnifying optical system comprising:
 an optical element that is a prism refracting an optical path, an aspect of the prism on an object-side including straight edges symmetrical with respect to an optical axis; 
 a first lens that includes planes parallel with the optical axis and symmetrical with respect to the optical axis, and includes a concave aspect facing the object-side of the optical element, a perimeter of the planes abutting the straight edges of the aspect of the optical element, and 
 a second lens that includes a concave aspect facing an image side of the optical element with a radius of the second lens being smaller than a radius of the image side of the optical element and abuts the image side of the optical element. 
 
     
     
       2. The reflex, magnifying optical system according to  claim 1 , wherein
 the first lens has a negative refractive power and an aspheric surface on both sides, 
 and 
 the second lens includes two lenses abutting each other and has a negative refractive power. 
 
     
     
       3. The reflex, magnifying optical system according to  claim 2 , comprising four lens groups,
 wherein a first lens group consists of:
 the first lens; 
 the optical element; and 
 the second lens, 
 
 a second lens group consists of three lenses and has a positive refractive power, 
 a third lens group consists of a single lens and has a negative refractive power, and 
 a fourth lens group consists of a single positive lens with a convex aspect facing toward an image. 
 
     
     
       4. The reflex, magnifying optical system according to  claim 3 , wherein at least two lenses of the second lens group are cemented together.